Deflecting coil for cathode ray tubes



March 2s, 1939. E* RUSKA 2,152,362

DEFLECTING COIL FOR CTHODE RAY TUBES I Filed Sept. 16, 1936 Patented Mar. 28, 1939 PATENT oFFlcE DEFLECTING COIL FOR CATHODE- RAY TUBES Ernst vRuska, Berlin-Zehlendorf, Germany, as-

signor to the firm Fernseh Aktiengesellschaft, Zehlendorf, near Berlin, Germany Application September 16, 1936, Serial No. 101,173 In Germany September 30, 1935 `5 claims. (ol. 25o- 156) In cathode ray tubes such as for example oscillograph tubes and television transmitting and receiving tubes the problem arises of deecting the ray free from distortion in one or in a y number of directions. lIt is especially true, when the ray is not sharply bundled together, as is the case in ordinary television receiving tubes or in tubes using a photocell mosaic, so that the ray has a large cross-section'as'in the Farns- `worth image scanning tubes using a photocathode, that it is difficult to produce magnetic fields having an adequately homogeneous shape in the entire deflectional space. If the deflection in addition is to be effected at high frequency and of l adequate sensitivity so'as 'to-permit use of fewer ampere turns,4 the coil system lused for producing the deflecting field must have dimensions which are as small as possible. The conductors of the coil must therefore be disposed as close asv possible to the space in which the ray moves, without deleteriously affecting the homogeneity of the eld in this space. f'

It is already known to make the deflecting coils in the form of rectangular coils and so to dispose them on both sides of the tube neck of a Braun tube that together they form a rectangular frame surrounding the neck of the tube. The longitudinal conductors in that case lie in two planes on both sides of the neck of the tube. In such an arrangement, however, the eld in the delecting space is not homogeneous since the lines of force in the vicinity of the tube axis are forced together and tend to deviate outwardly in a spread-apart manner.

In accordance with the invention a homogeneous field is produced by means of coils constructed in a special manner. The coil is so formed that the longitudinal conductors which produce the deflecting field together constitute the casing of a cylinder disposed coaxial to the direction of the principal ray. The coil is so wound that on one side of an axial section taken through this cylinder the current iiows only in one direction and on the other side only in the other direction. The electrical axis of the coil therefore lies in this section and is perpendicular to the aXs of the cylinder or tube.

The longitudinal conductors are preferably noneuniformly distributed on the casing surface and in such a manner that the current layer projected on the axial section and passing through the electrical axis of the coil is constant. Such a distribution of the winding permits the production of a Very homogeneous eld insi-de the coil space.

In some case it is desirable to give the deflecting eld a shape in which the lines of force do not run parallel but rather converge or diverge in a definite manner. Such an arrangement is desirable e. g. when the deflection is ggA not to be effected with uniform strength over the deecting sp-ace, so as for example to describe a rectangular surface (not a trapezoidal surface) upon an obliquely reposing screen. In such a case, by suitably distributing the windings on the periphery of the cylinder, the desired.I shape may be given to the deflecting field.

Embodiments are illustrated in the figures of the drawing.

Fig. 1 is a cross section through a deflecting coil and the deflecting space.

Fig. 2 is a schematic side view of the coil of Fig. 1 taken in the direction of arrow A.

Fig. 3 is across section through two deflecting coils pushed into each other, each being turned Fig. 4 isa cross section through a coil by means of which the eld is compressed in one direction.

The coil shown in Figs. l and 2 and provided with longitudinal conductors I and side conductors 2 produces a homogeneous field 3 in its interior. A dividing surface 4 may be passed through the electrical axis of the coil said surface lying perpendicular to the axis of' the cylinder or tube. The portions of the side conductors 2 lying between the pairs of longitudinal conductors are preferably so bent around that they lie outside the cylindrical internal space formed by the longitudinal conductors. As shown in the schematic representation of Fig. 2 the windings which constitute the side conductors 2 are closer together than the windings of the longitudinal conductors l and the separations between the windings of the side conductors are uniform.

If the arrangement is such that the side conductors 2 lie within the cylinder exteriorly enshrouding the longitudinal conductors, two of the tubular coils 5 and 6 may be pushed into each other as shown in Fig. 3. The axis of 45 coil 5 may then be displaced 90 with respect to the axis of coil 6. The arrangement in this case is preferably so chosen that the coils may subsequently be displaced with respect to each other at least to a small angular amount. In order to obtain as homogeneous a eld as possible, the longitudinal conductors are not distributed in a constant manner on the periphery of the circular cylinder, but in such a manner that the separation of the conductors or conductor groups projected on the axial section is constant for the same total current, as indicated in Fig. 1 by the heavier and lighter crosses and circles. The individual conductors are therefore distributed in varyingly dense manner and in such a manner that the windings of longitudinal conductors I which are furthest removed from the axis of the coil, lie closely against each other. The closer the longitudinal windings approach the axis of the coil, the more does the separation between the individual windings of longitudinal conductors I increase.

In order to give the magnetic elds produced by coil 2 a shape such as is indicated for example in Fig. 4, an unsymmetrical distribution of the windings is used with respect to the cross section plane 1 in accordance with the crosses and points shown in Fig. 4.

'Ihe coil of the invention may also be disposed within the tube, for which purpose it s mounted preferably on a ceramic member provided with recesses and/or grooves for receiving the individual wires or groups of Wires. A suitably shaped carrier for holding the coil may also be used exteriorly of the evacuated tube.

In some cases it may be preferable to form the coil as a cone in order to be able to enshroud all of the space occupied by the deflected ray as closely as possible.

I claim:

1. In combination with a cathode ray tube, means for producing a ray deflecting iield having a controlled intensity distribution in a plane normal to the undeflected ray axis, comprising deflecting coils having a plurality of turns, each turn having a plurality of turns, each turn having side conductors disposed parallel to the undeflected ray axis of said tube and end conductors concentric about said axis, said side conductors defining a cylindrical surface.

2. In combination with a cathode ray tube, means for producing a ray deliecting field having a controlled intensity distribution in a plane normal to the undeected ray axis, comprising deflecting coils having a plurality of turns, each turn having a plurality of turns, each turn having side conductors parallel to, and end conductors concentric about the undeiiected ray axis of said tube, said coils being so bent around the axis of said tube that said side conductors define a cylinder and are evenly spaced around the cylinder thus defined.

3. In combination with a cathode ray tube having a conical shape, means for producing a ray deiiecting iield having a controlled intensity distribution in planes normal to the undefiected ray axis, comprising deflecting coils having a plurality of turns, each turn having a plurality of turns, each turn having side conductors disposed along elements of a core whose axis is the axis of the undeiiected ray and end conductors concentric about the undeiiected ray axis of said tube, said coils being so formed about the axis of said tube that said side conductors define, and are evenly spaced about, a conical surface coaxial with said tube.

4. In combination with a cathode ray tube, means for producing a ray-deflecting iield of uniform strength in a plane normal to the undeiiected ray axis, comprising deflecting coils having a plurality of turns, each turn having a plurality of turns, each turn having end conductors concentric about said axis, and side conductors parallel thereto, said end conductors being so bent about said axis that said side conductors define a cylindrical surface, said side conductors being evenly distributed about the surface so defined.

5. In combination with a cathode ray tube having opposed deecting coils formed thereabout with side conductors parallel to, and end conductors concentric about the undeliected ray axis, said side conductors being positioned to define a cylinder concentric about said axis. means for producing a more intense field on one side of Said coils and symmetrical about a plane dividing said opposed coils, comprising a concentrated side conductor spacing on the side adjacent the desired intense iield.

ERNST RUSKA. 

